Herpetology Notes, volume 9: 55-58 (2016) (published online on 17 February 2016)

Arboreal behaviours of Crotalus cerastes (Hallowell, 1854) (Squamata, Viperidae)

Andrew D. Walde1,*, Andrea Currylow2, Angela M. Walde1 and Joel Strong3

Crotalus cerastes (Hallowell, 1854) is a small study area has no uninterrupted sandy areas outside of horned rattlesnake that ranges throughout most of the ephemeral washes, and no dune-like habitats. It is in deserts of southwestern United States, and south into this scrub-like habitat that we made three observations northern Mexico (Ernst and Ernst, 2003). This species of the previously undocumented arboreal behaviour of is considered to be a psammophilous (sand-dune) C. cerastes. specialist, typically inhabiting loose sand habitats and On 7 April 2005 at 1618h, we observed an adult C. dune blowouts (Ernst and Ernst, 2003). Although C. cerastes coiled in an A. dumosa shrub approximately 25 cerastes is primarily a nocturnal snake, it is known to cm above the ground (Fig. 1 A). The air temperature be active diurnally in the spring, and to bask in early was 21 °C and ground temperature was 27 °C. The morning or late afternoon (Ernst and Ernst, 2003). snake did not attempt to flee at our approach, but did This rattlesnake species exhibits a unique style of reposition slightly in the branches. A second observation locomotion known as sidewinding, from which it occurred on 18 April 2005 at 1036h, when we observed derives its common name, Sidewinder. Sidewinding is another adult C. cerastes extending the anterior third of believed to be an adaptation to efficiently move in loose its body beyond the top of an A. dumosa shrub (Fig. sand while reducing contact with the hot desert surface 2). The air temperature was 22 °C and the ground (Ernst and Ernst, 2003). However, during the past 12 temperature was 36 °C. Shortly after being observed, years of surveying in the Mojave Desert at the National the snake returned to the ground and took shelter at the Training Center, Fort Irwin, California, approximately base of a L. tridentata shrub. Finally, we observed this 40 km northeast of Barstow, San Bernadino County, we behaviour again on 3 May, 2007 (Fig. 1B). This third frequently observed C. cerastes in what is considered adult snake was approximately 40 cm from the ground typical desert scrub habitat. This area primarily in a California Jointfir (Ephedra californica); no time or comprises alluvial fans and washes with gravelly temperature data were recorded. soils dominated by Creosote (Larrea tridentata) and Rattlesnakes are not considered to be arboreal due to Burrobush (Ambrosia dumosa). The study area is having relatively stout, heavy bodies and short tails. described in more detail in Walde et al. (2009) and However, many species of rattlesnakes have been Harless et al. (2009). The habitat differs from the loose observed in shrubs and trees (Cunningham, 1955; sandy areas where C. cerastes is typically found, as the Klauber, 1997), with some species like the Timber Rattlesnake (C. horridus) frequently observed in arboreal situations (Saenz et al., 1996; Coupe, 2001; Rudolph et al., 2004). Although arboreal behaviour in the genus Crotalus has not been well studied, previously published explanations for the rare behaviour include: 1 Walde Research & Environmental Consulting, 8000 San to escape from water and flooding, to thermoregulate Gregorio Rd., Atascadero, CA 93422 (Shine et al., 2005), to capture prey (as would be 2 Department of Biological Sciences, University of Southern typical for bird nests; Martins et al., 2008), or to obtain California, Los Angeles, California, USA an advantageous perch in search of prey or enemies 3 Kleinfelder, 3919 Riga Boulevard, Tampa, Florida 33619, USA (Klauber, 1997). Juveniles and subadults of several * Corresponding author e-mail: [email protected] species more frequently use arboreal habitat than adults, 56 Andrew D. Walde et al.

to the cooler ground. Fitzgerald et al. (2003) described a correlation between perch height, air temperature, and preferred body temperatures in Stephen’s Banded Snakes (Hoplocephalus stephensii), finding that the snakes would adjust their perch height to maintain preferred temperatures with changing air temperatures. Although C. cerastes typically bask on the ground, often in self-constructed depressions, it is possible that the snakes in the first and third observations were aerially basking in an attempt to avoid heat loss to the cooler ground. Although 2005 had a relatively wet spring (Harless et al., 2009) that might have caused the ground to be cooler and moister than normal for the time of year, 2007 was a drought year in the Mojave Desert and it was abnormally dry. Therefore, the behaviour may be more common than previously thought for the species and not correlated with moisture. The second snake we observed in 2005 was perched high in a small A. dumosa shrub when ground temperatures were higher, so it is possible that the snake could have been using the shrub to escape heat on the ground. However, the snake could have been both thermoregulating high in the shrub while also exhibiting vigilance behaviour. Klauber (1997) observed that rattlesnakes may use vegetation to obtain an advantageous perch in order to search for enemies. Figure 1. Adult Sidewinders (Crotalus cerastes) coiled, using Fitzgerald et al. (2003) suggested that snakes may arboreal resting sites in (A) a Burrobush (Ambrosia dumosa) not use open terrestrial basking sites in order to avoid and (B) a California Jointfir (Ephedra californica) in the predation if there are vegetative basking sites available. Mojave Desert, California, USA. The second snake’s posture and behaviour suggested it was surveying the area, similar to spy-hopping in whales or scanning, anti-predator vigilance behaviours. The protection from predation offered by basking in a shrub may allow the chiefly nocturnal snake to rest in the daytime. with foraging proposed as the most likely purpose (C. The only two previously reported observations of horridus: Rudolph et al., 2004; C. oreganus helleri: Sidewinders utilising shrubs include an individual which Figueroa et al., 2008). retreated into a low shrub after being harassed (Klauber, During the time of our observations, no flooding or 1997), and a captive specimen in a laboratory which pooled water was present that might have prompted was coiled in a shrub in its enclosure (Cunningham, climbing. There were no bird nests in the shrubs to 1955). Cunningham (1955) attributed the behaviour, suggest foraging; however, lizards frequently climb however, to the setup of the enclosure itself, as at a later into shrubs, and the snakes might have followed them date another species of rattlesnake housed in the same or their odours. Temperatures recorded at the time of enclosure also coiled in the same shrub. Similarly, in our observations do not necessarily suggest that these a study on elapid snakes in Australia, Fitzgerald et al. snakes were attempting to escape the heat of the desert (2003) found that snakes in a captive setting would often surface. In field observations followed by controlled behaviourally thermoregulate arboreally, but would trials of the thermoregulatory-arboreal behaviour rarely exhibit the behaviour in the natural field setting, of Red-sided Garter Snakes (Thamnophis sirtalis motivating the authors to caution against extrapolating parietalis), Shine et al. (2005) found that the snakes captive results for natural wild behaviours. would climb trees when there was a risk of heat loss The earliest reports of arboreal habitat use by Arboreal behaviours of Crotalus cerastes 57

Figure 2. An adult Sidewinder (Crotalus cerastes) extending its head from a Burrobush (Ambrosia dumosa) in the Mojave Desert, California, USA.

rattlesnakes included these species: C. adamanteus, C. reports document chance observations or if arboreal atrox, C. enyo, C. horridus, C. mitchellii, C. molossus, habitat use is a well-developed behaviour. Klauber C. oreganus, C. ruber, C. tigris, C. viridis, and Sistrurus (1997), more than 50 years ago stated that any species miliarus streckeri (Cunningham, 1955; Klauber, of rattlesnake observed long enough would, at some 1997). Since these early reports, others have reported point, probably be observed in a tree or shrub. Here, we observations of some of these same species in arboreal add the Sidewinder to this growing list of observations. habitats, for example C. enyo cerralvensis (McGuire, Funding for the project during which these observations 1991) and C. tigris (Pavlik, 2007); however, by far were made was provided by USACERL/ERDC in the most arboreal rattlesnake appears to be C. horridus Champaign, Illinois and DPW Environmental at the (Saenz et al., 1996; Coupe, 2001; Rudolph et al., 2004). National Training Center, Fort Irwin, California. More recent observations of rattlesnakes using arboreal habitat include C. cataliensis (Martins et al., 2008), C. durissus (Dayrell et al., 2010), C. mitchellii (Evanhoe Literature Cited and Haug, 2011), C. ruber lorezoensis (Hollingsworth Coupe, B. (2001): Arboreal behavior in Timber Rattlesnakes and Mellink, 1996), C. willardi obsurus (Holycross et al., (Crotalus horridus). Herpetological Review 32: 83–85. 2002), and C. willardi willardi and C. lepidus klauberi Cunningham, J.D. (1955): Arboreal habits of certain reptiles and (Rossi and Feldner, 1993). It remains unknown if these amphibians in Southern California. Herpetologica 11: 217–220. 58 Andrew D. Walde et al.

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Accepted by Benjamin Tapley